This might help you out. If you're using google chrome, go to the settings > history > clear browsing data and you will see somewhere "Time range" or however is it on yours language, set it "All time". So it will permanently delete all yours history/cache and you should be able to login/register on imgur. That is only one solution you can do for now. If you have problem with the browser (google chrome), try to switch on Mozilla or so on.

I hope this helped, because back then I had same issue, and when I deleted all history from my browser, it really worked.

This might help you out. If you're using google chrome, go to the settings > history > clear browsing data and you will see somewhere "Time range" or however is it on yours language, set it "All time". So it will permanently delete all yours history/cache and you should be able to login/register on imgur. That is only one solution you can do for now. If you have problem with the browser (google chrome), try to switch on Mozilla or so on.

I hope this helped, because back then I had same issue, and when I deleted all history from my browser, it really worked.